JPH06114842A - Film removing method - Google Patents

Abstract

PURPOSE:To provide a film removing method capable of safely performing work as compared with the prior art method and capable of reducing the amt. of salts formed in a waste water neutralizing method by using a neutral or weak alkaline aqueous release soln. easy to handle without using a release soln. containing an org. solvent or a strong alkaline release soln. CONSTITUTION:A substrate having a cured film on the surface thereof is treated in a neutral or weak alkaline aqueous release soln. (pH; 7.5-9.5) at temp. equal to or higher than 110 deg.C but lower than the temp. dissolving the substrate to remove the cured film from the surface of the substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing a coating film, which is treated with a neutral or weak alkaline aqueous solution which is easy to handle, without using an organic solvent or a strong alkaline stripping agent which causes environmental problems. The present invention relates to a method capable of chemically removing a coating film on a substrate.

[0002]

2. Description of the Related Art Generally, resin molded products have advantages such as light weight and excellent impact resistance as compared with metal products, glass products, etc., and they are inexpensive and easy to mold. , Automobiles, home appliances, daily necessities, and many other fields. Particularly in the automobile industry, the number of resin parts occupying the vehicle body tends to increase year by year in order to reduce the weight of the vehicle body.

Many of these resin molded products are coated for the purpose of improving corrosion resistance and weather resistance and improving the appearance of the products.
As the coating material used for this coating, many materials that form a three-dimensional cross-linked coating film are used in terms of the adhesiveness to a resin molded product and the performance of the coating film itself. However, due to this excellent coating performance, when it is necessary to peel the coating for some reason, the coating having a strong crosslinked structure is not easily peeled.

On the other hand, the peeling of the coating film is to reuse only the resin base material of the resin molding product to be coated when a defect occurs in the coating process or when the old coating film having deteriorated performance is replaced with a new coating film. It is an important industrial technology that is required in many industrial situations.

Conventionally used methods for peeling and removing coating films are roughly classified into physical peeling and chemical peeling. Of these, physical peeling is a method of scraping the coating film with a sandpaper or the like.

Chemical peeling can be roughly divided into the following three types. 1) Removal with a release agent containing a chlorine-based solvent as a main component (JP-A-51-34238, JP-A-57-76065, and JP-A-59-117567). 2) Removal by a release agent containing an organic substance as a main component (JP-A-57-190675, JP-A-1-289878, and JP-A-2-274775). 3) Removal by a release agent containing an inorganic substance as a main component (JP-A-50-109925, JP-A-53-35735, JP-A-61-2162568). There is also a removal method using a stripping agent obtained by arbitrarily mixing the main components of the above-mentioned three types of stripping agents, or a stripping agent obtained by arbitrarily mixing these with other components.

[0007]

However, the physical peeling method is inefficient because it requires a considerable amount of time when the substrate is scratched or a large amount of the coating film is peeled off. On the other hand, in the method of chemical peeling, all of the peeling agents of the method 1) have excellent peeling performance, but the peeling agent may corrode the substrate itself depending on the substrate. In addition, it is well known that chlorine-based solvents have an adverse effect on the human body, and regulations on these chlorine-based solvents are becoming stricter year by year from the standpoint of environmental protection, making it difficult to use these chlorine-based solvents in the future. Is. The organic substances used in the method 2) are various alcohols, amine type compounds and the like, and like the chlorine-based solvent used in the method 1), there is a risk of adversely affecting the environment and the human body. 3)
Many of the stripping agents used in the method (1) have an alkaline substance as a main component. However, such strippers have a fairly high pH (pH = about 13-14).
Since strong alkali dissolves fat, it will corrode the skin etc. if it adheres to the human body. In addition, when a strong alkaline substance such as NaOH or KOH is dissolved, the pH of the solution becomes 13 to 14 even if the dissolved amount is as small as 0.1% by weight. In order to obtain a neutral or weakly alkaline stripping solution, the amount of strongly alkaline substances dissolved must be very small, and although a stripping solution with a low pH can be obtained, it is insufficient in terms of stripping performance. Inevitably. Furthermore, the high pH stripping agent is neutralized with an acid after use and discarded, but it is not environmentally preferable that the sodium chloride or the like produced by the neutralization is wasted. Especially when wastewater is discharged into rivers, it is necessary to take measures such as diluting the concentration with a large amount of water or removing the salt by evaporating the water in order to reduce the amount of salt to below the standard value of wastewater. The amount of water and the cost required for it are enormous. Therefore, there has been a strong demand for a method or a peeling agent having a pH value in a neutral region or a weak alkaline region and capable of sufficiently peeling a coating film from a substrate.

Therefore, the object of the present invention is to use a neutral or weakly alkaline aqueous stripping solution which is easy to handle, without using a stripping solution containing an organic solvent or a strong alkaline stripping solution, thereby providing a conventional method. The present invention relates to a method for removing a coating film, which is capable of safely performing work as compared with the above-mentioned method and which can reduce the amount of salts produced in the neutralization step of wastewater.

[0009]

In order to solve the above-mentioned problems, the present invention immerses a substrate having a cured coating film on its surface in a neutral or weakly alkaline aqueous stripping solution to form a substrate at 110 ° C or higher. The present invention provides a method for removing a coating film, in which the cured coating film is peeled and removed from the substrate surface by treating at a temperature lower than the melting temperature.

The pH of the neutral or weakly alkaline aqueous stripping solution is preferably 7.5 to 9.5.

It is preferable that the neutral or weakly alkaline aqueous stripping solution is an aqueous solution in which one or more alkaline substances having a desired pH value are dissolved in water. .

The alkaline substance is NaHCO 3.₃, K
HCO₃, Na₂B_FourO₇And K ₂B_FourO₇Choose from
It is preferable that it is at least one kind.

The neutral or weakly alkaline aqueous stripping solution is preferably an aqueous solution in which an acidic substance and an alkaline substance are dissolved.

It is preferable that the acidic substance is boric acid.

The alkaline substance is NaOH or KO.
H, LiOH, Ca (OH)₂, Na ₂B_FourO₇, K₂
B_FourO₇, NaAlO₂, Na₂CO₃And K₂CO
₃It is preferable that it is at least one selected from

It is preferable to carry out the treatment at a temperature of 140 ° C. to 160 ° C.

It is preferable that the substrate is made of polyolefin, especially polypropylene.

Hereinafter, the method for removing the coating film of the present invention (hereinafter, referred to as
"Abbreviated as" method of the present invention ") will be described in detail.

The method of the present invention is a method of removing a cured coating film formed on the surface of a substrate. This substrate is not particularly limited, and the method of the present invention may be applied to a substrate made of any material. In particular, the method of the present invention is effective in removing the coating film on the surface of the substrate made of polyolefin.
The polyolefin is not particularly limited and is a homopolymer of α-olefin; a copolymer of two or more types of α-olefin; a modified product of these polymers or copolymers; or a polymer or copolymer thereof. And a polymer having another polar group. Examples of the α-olefin include ethylene, propylene, 1-butene, 1
-Pentene, 2-methyl-1-butene, 3-methyl-1
-Butene, 1-hexene, 4-methyl-1-pentene,
3-methyl-1-pentene, 2-methyl-1-pentene, 1-heptene, 4-methyl-1-hexene, 1-octene, 5-methyl-1-heptene, 1-decene and the like can be mentioned. Specific examples of polyolefins composed of these α-olefins include polyethylene, polypropylene,
Examples thereof include polybutene and poly-4-methyl-1-pentene.

As modified products of α-olefin homopolymers or copolymers of two or more α-olefins, for example, maleic acid, fumaric acid and citracone are added to these homopolymers or copolymers. Examples thereof include unsaturated carboxylic acids such as acids, itaconic acid and hymic acid, and graft modified polymers obtained by graft-copolymerizing anhydrides of these unsaturated carboxylic acids and alkyl esters.

Further, as a polymer having a polar group mixed with these homopolymers or copolymers, a copolymer of α-olefin and a polar group-containing monomer, for example, ethylene / vinyl acetate copolymer, ethylene Examples thereof include (meth) acrylic acid and ester copolymers and ethylene / vinyl alcohol copolymers.

Among the substrates made of these polyolefins, particularly when the molded product made of polypropylene is the substrate, when the cured coating film on the surface of the substrate is removed, the substrate is not damaged at all and the treatment is not required. The method of the present invention is effective because the physical properties of the substrate do not deteriorate before and after.

Further, according to the method of the present invention, the shape of the substrate at the time of removing the coating film is such that the interface between the substrate and the coating film is exposed and the area in contact with the peeling liquid increases, so that the peeling of the coating film is efficient. From the viewpoint of being often performed, it is preferably powdery.

As the cured coating film peeled by the method of the present invention, for example, a coating material such as a phenol-based coating material, a polyester-based coating material, an alkyd-based coating material, an acrylic-based coating material, a polyurethane-based coating material or an epoxy-based coating material is applied and cured. The things that can be done are listed. In particular, the method of the present invention is suitable for peeling a cured coating film having a structure in which an acrylic resin, an alkyd resin, a polyester resin or the like used for coating automobiles is crosslinked with melamine.

The neutral or weak acid used in the method of the present invention
For the preparation of aqueous solution of Lucari, dissolve it in water
One or two alkaline substances in which the liquid has a desired pH value
A first method of dissolving one or more species in water can be mentioned. This person
Examples of the alkaline substance used in the method include Na
₂HPO_FourPhosphates such as NaHCO₃, KHCO₃etc
Bicarbonates, organic acid salts such as sodium acetate, Na₂B_Four
O₇, K₂B_FourO₇And the like, and the like. this
Among them, NaHCO₃, KHCO₃, Na ₂B_FourO
₇, K₂B_FourO₇Is preferred. We also prepared an aqueous stripper
The second method is to use an acidic substance and an alkaline substance.
Method of dissolving in water at an arbitrary ratio to adjust to a desired pH value
Can also be mentioned. As an acidic substance used in this method
Is one that does not show strong acidity when dissolved alone in water
However, it is preferable because the pH can be easily adjusted.
Inorganic salts such as uric acid, organic salts such as acetic acid, NaH₂PO_FourEtc.
Organic acid salts such as phosphate and potassium hydrogen phthalate are listed.
You can Among these, boric acid is cheap because it is cheap.
preferable. As the alkaline substance, the above-mentioned first
Examples of alkaline substances used in the method
In addition, NaOH, KOH, LiOH, Ca
(OH) ₂Such as hydroxide, Na₃PO_FourPhosphates, etc.
NaAlO₂Aluminate such as Na₂CO₃, K₂C
O₃And the like. Among these, N
aOH, KOH, LiOH, Ca (OH)₂, Na₂C
O₃, K₂CO₃, Na₂B_FourO₇, K₂B_FourO₇, N
aAlO₂Dissolve one type alone or a combination of two or more types.
Aqueous stripping solution prepared by adjusting the pH value
It is preferable because it can exhibit excellent peeling performance. It
In addition, the aqueous stripper, as a pH adjuster or accelerator
A small amount of neutral salt such as KCl may be added.

P of the aqueous stripper used in the method of the present invention
With H, the coating film is sufficiently peeled off and there is no adverse effect on the human body,
Moreover, when the used aqueous stripping solution is disposed of, the pH adjustment in the wastewater treatment is not necessary, and it is effective in reducing the cost of the wastewater treatment. It is preferably in the range of 0.5 to 9.5.

In addition to the alkaline substance, the aqueous stripper may optionally contain other compounding agents. For example, a small amount of a surfactant, ammonia, amines, an organic solvent or the like may be contained as a processing accelerator. Examples of the surfactant include alkylbenzene sulfonates, dialkylsulfosuccinates, polyoxyethylene alkyl ethers and the like, and examples of amines include alkylamines such as triethylamine and alkanolamines such as monoethanolamine. And so on. Examples of the organic solvent include methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2
-Propyl alcohol, t-butyl alcohol and the like having good compatibility with water can be mentioned.

In addition, a preservative such as sodium azide may be included.

In the method of the present invention, the method of treating the substrate with the aqueous stripping solution is not particularly limited, and a method of immersing the substrate in the aqueous stripping solution or a method of treating the substrate in the aqueous stripping solution under pressure in an autoclave. It can be performed by a dipping method or the like. Moreover, it is preferable to perform stirring during the immersion. When the treatment is performed under pressure, the pressure is about 4 to 5 kg / cm ² at a temperature of 150 ° C.

In the method of the present invention, the temperature for treating a substrate having a cured coating film on its surface with an aqueous stripper is 110
The temperature is lower than the temperature at which the substrate melts at a temperature of ℃ or more, usually 110 to 170 ℃, preferably 140 to 16
It is 0 ° C.

Further, the treatment time may be appropriately selected according to the type of cured coating film, the film thickness, the shape and size of the substrate, or the treatment temperature, and is usually 10 minutes to 2 hours, preferably 30 minutes to. It takes about 1.5 hours.

In the method of the present invention, the substrate is treated with an aqueous stripping solution to release the cured coating film, and the coating film residue adhering to and remaining on the substrate surface is removed to obtain a cured coating film on the surface. A removed substrate can be obtained.

As described above, the substrate from which the cured coating film has been removed by the method of the present invention is again formed with a cured coating film in the coating step to make a product, or pelletized as a raw material resin for various processed products. Can be reused.
Further, the aqueous stripping solution used for the stripping treatment can be repeatedly used by removing the coating film or the residue thereof in the stripping solution by a method such as filtration.

[0034]

EXAMPLES The present invention will be specifically described below with reference to Examples of the present invention and Comparative Examples, but the present invention is not limited to these Examples.

(Examples 1 to 8 and Comparative Examples 1 to 4) In each example, polypropylene containing 0.5% by weight of carbon black (manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: HYPOL, hereinafter PP) (Abbreviated) was subjected to injection molding to prepare a square plate having a thickness of 3 mm. The square plate was subjected to 1,1,1-trichloroethane vapor cleaning for 30 seconds, and then left at room temperature for 30 minutes to be dried. Next, the square plate 1,1,1-
On the surface washed with trichloroethane, a primer (UNISTOL P-80, manufactured by Mitsui Petrochemical Industry Co., Ltd.)
1) was applied using a spray gun so that the primer film thickness after drying would be about 10 μm, and then 10
The setting was performed for a minute to form a primer film.
After that, a thermosetting paint (Kansai Paint Co., Ltd., one-component acrylic melamine-based paint, Soflex # 1200) was sprayed onto the primer film on the square plate with a spray gun (discharge pressure 3 k).
g / cm ² ) and the thickness of the cured coating film is 20 to 40 μm.
It was applied so as to have a thickness of m and set for 10 minutes. Then, the coating film was cured by heating at 120 ° C. for 30 minutes to obtain a sample piece having a cured coating film on the surface of a polypropylene square plate.

The obtained sample piece was crushed to a diameter of about 5 mm (hereinafter referred to as "sample"), placed in an autoclave filled with an aqueous stripping solution having the composition and pH shown in Table 1, and immersed in the aqueous stripping solution. Then, the treatment was carried out by stirring at the treatment temperature shown in Table 1 for 1 hour. Then, it was cooled to room temperature, the sample was separated from the aqueous stripping solution, washed with water and dried, and the state of peeling of the coating film was observed. Aqueous stripper treatment at high temperature requires high pressure (4-5 kg / c
Using the autoclave to become m ^2).

Regarding the peeling state of the coating film, the presence of the coating film was examined by visually observing the sample before washing with water. When there was a sample with a coating film remaining, the coating film was rubbed with a finger or scratched with a nail to check the ease of peeling of the coating film, and evaluated according to the following criteria. The results are shown in Table 1. ◎: Spontaneous peeling during stirring ×: No peeling

[0038]

(Example 9) Poly-4-methyl-1-pentene (manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: TPXMX-
After applying a primer to the injection-molded rectangular plate (thickness: 3 mm) made of 004) by the method described in Example 1,
A coating film was formed to prepare a sample piece.

The obtained sample piece was crushed to a diameter of about 5 mm to prepare a sample, and the sample was placed in an autoclave filled with a 3% NaHCO ₃ aqueous solution (pH = 8.1), and the sample was placed at 150 ° C. for 30 minutes. After stirring and peeling,
The coating film was completely removed.

[0041]

According to the method of the present invention, a cured coating film formed on the surface of a substrate can be treated with an aqueous stripping solution having a lower pH value than that obtained by the conventional method without using an organic solvent having an environmental problem. Can be easily peeled off. Moreover, in the method of the present invention, the aqueous stripping solution used can be repeatedly used, and the amount of salts produced in the neutralization step when discarding the processing solution can be reduced, which is industrially useful. is there.
Therefore, the method of the present invention fails to form a desired cured coating film, for example, when the cured coating film once formed is removed from the substrate and the coating film is formed again, and also in the substrate having the cured coating film on the surface. Since the substrate is reused, it is effective when the cured coating film is removed from the substrate.

Claims (10)

[Claims] 1. A substrate having a cured coating film on its surface is treated in a neutral or weakly alkaline aqueous stripping solution at a temperature lower than 110 ° C. and lower than the temperature at which the substrate dissolves to give a cured coating film on the substrate surface. A method of removing a coating film that is peeled off and removed. 2. The method for removing a coating film according to claim 1, wherein the neutral or weakly alkaline aqueous stripping solution has a pH of 7.5 to 9.5. 3. The neutral or weakly alkaline aqueous stripping solution is an aqueous solution in which one or more alkaline substances having a desired pH value are dissolved in water. ,preferable. 4. The alkaline substance is NaHCO 3.₃, K
HCO₃, Na₂B_FourO₇And K ₂B_FourO₇Choose from
The removal of the coating film according to claim 3, which is at least one of
Method. 5. The method for removing a coating film according to claim 1, wherein the neutral or weakly alkaline aqueous stripping solution is an aqueous solution in which an acidic substance and an alkaline substance are dissolved. 6. The method according to claim 1, wherein the acidic substance is boric acid.
6. The method for removing a coating film according to any one of 5 and 5. 7. The alkaline substance is NaOH or KO.
H, LiOH, Ca (OH)₂, Na ₂B_FourO₇, K₂
B_FourO₇, NaAlO₂, Na₂CO₃And K₂CO
₃6. At least one selected from the group consisting of:
7. The method for removing a coating film according to any one of 6 and 6. 8. The method for removing a coating film according to claim 1, wherein the treatment is performed at a temperature of 140 ° C. to 160 ° C. 9. The method for removing a coating film according to claim 1, wherein the substrate is made of polyolefin. 10. The method for removing a coating film according to claim 9, wherein the polyolefin is polypropylene.